Technical Field
The present invention relates to layered structures, and, more particularly, to thin film transistors used for image display devices.
Background Art
Amorphous silicon (a-Si) thin film transistors (TFT) and polysilicon (poly-Si) thin film transistors on glass substrates employing transistor and IC technologies that use semiconductors as substrates have been manufacturered. These thin film transistors are used for liquid crystal displays as switches (see Liquid Crystal Display Technology-Active Matrix LCD-, edited by Shoichi Matsumoto, Sangyo Tosho (Nov. 11, 1996)). When a TFT is turned on by a selected voltage being applied to a wire for the gate, a signal voltage supplied to a source wire is applied to a pixel electrode connected to the drain. The applied voltage is stored in a storage capacitor comprised of the pixel electrode, a gate insulating film, and a capacitor electrode.
For TFT arrays, the workings of the source and those of the drain change depending on the polarity of an applied voltage, and so calling their names by work may create confusion. Thus, for convenience, one side of each TFT is referred to as source, and another side thereof is referred to as drain. In the present invention, one side of a TFT connected to a wire is referred to as a source, and another side connected to a pixel electrode is referred to as a drain.
Recently, there have been developed oxide semiconductors and organic semiconductors, and TFTs can be manufactured at a low temperature of not more than 200° C. This raises hopes for flexible displays made with plastic substrates; these flexible displays being more light in weight, difficult to break, and able to be thin in addition to being flexible. It is hoped that cheap, large-area displays based on TFTs can be fabricated by printing.